Typically, in healthy humans and animals, their body's kidneys, amongst other organs, effectively remove excess water, salts, and toxins as well as breakdown materials, such as, proteins and other waste products (e.g., produced by metabolism) circulating in blood. Nearly 400,000 people in the United States of America, and as many as two million people worldwide suffer from kidney failure. This number is estimated to be increasing at annual rates of about 9%. In these individuals, their own kidney does not function properly and naturally produced wastes are not effectively removed.
Generally speaking, to restore such a patient to close to full health, a kidney transplant is needed. However, the present demand for kidney transplants is heavily outnumbered by the limited supply of donor organs. For example, as of 2011 there are about 85,000 patients in the United States of America on waiting lists for a kidney, while only about 17,000 kidney transplants took place in 2010. Even with a kidney transplant, complications such as host rejection and complications from immunosuppressive medications, which can be required to be taken for life to prevent rejection, is not uncommon. In addition, graft versus host and transplanted infectious diseases can also develop. Hence, in many patients with loss of kidney function (e.g., renal failure), the normal kidney cleaning process has to be performed artificially, for example, through external treatments such as dialysis, typically either hemodialysis or peritoneal dialysis.
In hemodialysis, for example, a patient's blood is typically re-routed outside the body to a dialyzer which filters the blood using disposable cartridges that include numerous substantially small, semipermeable, plastic membranes, with varying pore sizes. Using this technique, as blood diffuses through these membranes, contaminates are removed from the patient's blood in conjunction with a counter-current flow of a fresh dialysate solution. Toxins in the blood (e.g., salts and various unwanted low molecular weight molecules) preferentially diffuse across these membranes as a result of flow-induced or osmotic pressure differentials, resulting in reduced toxin concentrations. The now purified blood is then returned to the patient's body, usually via a vein in the arm and/or through the lumen of an inserted catheter.
While undergoing dialysis, patients are required to be connected to substantially large and expensive machines. For example, patients may typically be required to receive treatments at least three to four times a week, for about three to five hours at a time. Even then, dialysis machines may only be about 13% as effective as a fully functional kidney. Five-year survival rates of patients on dialysis has been estimated to be just 33-35%.
Further, when using dialysis, only about 10-40% of larger molecules, called middle molecular weight molecules, are removed during a given dialysis session. The ability to remove large molecular mass molecules merely by diffusion across a membrane is substantially decreased. This can lead to a buildup of larger-sized toxins within the patient's blood. Consequently, without removal, these toxins can reach abnormally high concentration levels and can damage the body over time. Some have speculated that inefficient removal of these toxins represents a significant limitation of current renal dialysis technology.
To achieve adequate removal of these toxins, manufactures and nephrologists have been attempting to increase surface areas of dialysis membranes and also prolong dialysis treatment times. However, there are limits to increasing surface areas of dialysis membranes. In addition, increased dialysis times coupled with the physical and social side effects of dialysis, can reduce the patient's quality of life and add prohibitive expense to people suffering from a loss of kidney function.